where \(\delta ^{\prime }\)  is the image of \(\delta \)  under the reflection \(s_{\gamma }\) 
in the hyperplane orthogonal to \(\gamma \)  and \(c = \pm 1\) 
(see Relation (R7) in [1]}).
Recall that \(s_{\gamma }\)  is given by
\(s_{\gamma }(\delta ) = \delta - 2 \frac{(\gamma ,\delta )}{(\gamma ,\gamma )} \gamma \, ,\) 
